The present disclosure relates to display devices and more particularly to display devices having touch screens.
User interface accessories for consumer electronics have migrated from conventional keyboards and similar hardware peripherals to so-called “virtual” user interfaces. The conventional keyboard is implemented using a resistance matrix fitted under an arrangement of mechanical buttons. The actuation of a selected mechanical button generates a unique row/column signal that is interpreted as a letter, number, or control function. While the conventional keyboard has been widely accepted in commercial use, it suffers from a number of limitations such as large size and inflexibility of application. These limitations are particularly manifest in relation to emerging electronic devices which are generally smaller and more portable than their commercial predecessors. As a result, virtual keyboards and other types of virtual user interfaces are increasingly incorporated into contemporary electronic devices, such as laptop Personal Computers (PCs), Personal Digital Assistants (PDA), tablet PCs, mobile phones, MP3 players, GPS navigators, etc.
Virtual user interfaces may be implemented using a number of different technologies, including, for example, resistive, capacitive, optical, inactive, infrared and surface acoustic wave. One particularly advantageous approach to the implementation of virtual user interfaces is the capacitive touch screen panel (TSP).
Capacitive TSPs enjoy performance and implementation benefits over competing technologies. Capacitive TSPs are highly stable, allow high data throughput, and enable multiple input modes of data input. Published U.S. Patent Publication 2007/0273560 describes one example of a capacitive TSP and is hereby incorporated by reference.
Referring to Figure (FIG. 1, a conventional touch screen panel (TSP) 10 includes a touch screen 4 overlaying a top plate 2. The touch screen 4 includes row and column elements coupled to corresponding sensor lines 6 and respective X/Y sensing circuits. A horizontally oriented parasitic capacitance 8 exists between adjacent sensor lines. A vertically oriented parasitic capacitance 9 exists between sensor lines 6 and top plate 2. A sensing capacitance 5 is developed between a conductive object 7 (e.g., a user's finger or stylus) and proximate sensor lines 6. This sensing capacitance 5 may be detected and subsequently interpreted by circuitry within the TSP 10 as a user input selection (i.e., a letter, number or control function).
Despite the many benefits afforded by capacitive TSPs, they suffer from several implementation and operational difficulties, such as an inability to recognize highly detailed input data (i.e., a limited ability to discriminate small aspect writing or symbol input), a high sensitivity to ambient noise, and physical size limitation.
As shown in FIG. 2, the physical size of a TSP may be generally expressed in terms of a diagonal dimension value “d”. Contemporary capacitive TSPs are limited to a physical size no greater than about ten (10) inches.
As is conventionally understood, the capacitive TSP of FIG. 2 includes a sensor array 20 of individually configured sensor elements 23 arranged in a defined matrix of rows and columns. The capacitive TSP may be formed from an indium thin oxide (ITO) material and the plurality of sensor elements 23 may be arranged in a diamond pattern within the sensor array 20. The capacitive TSP includes so-called Y-direction conductive lines 22 and X-direction conductive lines 24, respectively communicating user input data from the capacitive TSP to related computational circuitry.
Throughout the written description of this disclosure, certain terms like “horizontal” and “vertical”, or “X-direction” and “Y-direction” are used as relative geometric terms in conjunction with the accompanying drawings. Those skilled in the art will recognize that such terms are merely descriptive and are not intended to mandate some arbitrary layout of elements. Such terms are, however, useful in describing exemplary arrangements of elements in relation to the principle physical plane formed by the touch screen panel. Accordingly, the foregoing terms describe possible inter-elements geometries but do not mandate the particular layout orientation suggested by the accompanying drawings.
The relatively small, maximum size of conventional capacitive TSPs is a function of practical signal sensitivity limitations. As the length of the constituent row and column signal lines increases with an overall increase the physical size of the capacitive TSP, the number of sensor elements connected to each signal line also increases. The combination of additional noise and signal line impedance resulting from the increased number of connected sensor elements and the added length of the constituent signal line ultimately makes it difficult to accurately interpret user input data. As a result, capacitive TSPs have heretofore been limited to applications requiring only a relatively small display sizes.